Compare devices that change energy from one form to another
Grade 11 Science Worksheet - Challenge Me
Circle the best answer, or write your answer on the line.
Ari's hand-crank chain has stages of 25%, 80% and 90% efficiency. To store 450 J in a battery, how much work must go in?
Bo's hand-crank chain has stages of 40%, 88% and 50% efficiency. To store 2200 J in a battery, how much work must go in?
A steam engine runs between 500 K and 300 K. Its best possible efficiency is 1 − 300 ÷ 500. A designer claims 55%. Judge it, Jun.
- Impossible: the limit is 60%, from 300 ÷ 500
- Possible: 55% is below 100%
- Impossible: the limit is 40%
- Possible: less friction could reach 55%
A plant is 36% efficient, the grid delivers 94% and the motor is 90% efficient. About how much of the fuel energy does useful work, Kira?
- About 36%, the plant alone
- About 3.0%
- About 73%, the average of the three
- About 30%
From 100 units of fuel, a plant makes 30 units of electricity and 45 units of useful heat for homes. What share of the fuel is put to use, Luz?
- 25%, the share that is wasted
- 30%, counting the electricity alone
- 75%, counting heat and electricity
- 45%, counting the heat alone
An ad says "our electric heater is 100% efficient, so it wastes nothing." Most electricity comes from plants near 35%. Judge the claim, Milo.
- False: the heater itself wastes most of the energy it uses
- True at the heater, but 65% of the fuel energy was lost earlier
- True: no energy is lost anywhere upstream of the heater
- False: the heater converts nothing into heat as it runs
Noah wants to compare the efficiency of two motors. Which measurements are best?
- Each motor's top speed while it spins with no load
- The wattage printed on each motor's label plate
- How hot each motor gets after running for one minute
- Electrical energy in and work done on one load, for each
A battery pack is rated 95% round-trip. A test charges it with 500 Wh and gets 440 Wh back. Judge the rating, Pia.
- The test shows 88%, 7 points below the rating
- The test shows 12%, so the rating is far off
- The test shows 88%, which is close enough to 95%
- The test shows 95%, since 440 + 60 = 500
Engine X goes from 40% to 50% efficiency; engine Y goes from 80% to 90%. For 100 J of useful work, which saves more fuel energy, Tala?
- Both save the same, since each gains 10 points
- Engine Y saves more, since it is closer to 100%
- Engine X saves about 50 J; engine Y saves about 14 J
- Engine Y saves about 50 J; engine X saves about 14 J
Zee wants to find where a toy robot wastes the most energy. Which test is best?
- Measure the energy in and out of each stage
- Measure the energy in and the final speed alone
- Run the robot for longer and watch the battery
- Replace the parts with new ones at once